“But… this is one of the most critical humanitarian contexts and we will definitely do everything to continue our operations there.”

IS has been in Afghanistan since 2015, claiming attacks in Kabul and the east. But there has been no immediate claim for the attack in Jowzjan.

Image copyrightICRCImage captionThe ICRC has spent three decades assisting sick people in remote areas of Afghanistan

The ICRC has had an uninterrupted presence in Afghanistan for 30 years and the organisation said in a tweet that it was “shocked and devastated” by the news. President Peter Maurer said it was a deliberate attack on his staff which “we condemn in the strongest possible terms”.

The team which came under attack by “unknown armed men” comprised three drivers and five field officers, the statement said.

Government officials said the staff were transporting supplies including livestock materials to areas affected by recent deadly snowstorms when their convoy was attacked.

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Jowzjan governor Lutfullah Azizi confirmed to the BBC that all six employees who were killed were Afghan.

The bodies of the six workers – many with close range multiple gunshot wounds – have been taken to the provincial capital Sheberghan, and a search has begun to find the two ICRC employees who have not been accounted for.

Provincial police chief Rahmatullah Turkistani said IS fighters were known to be active in the area where the attack took place.

Taliban militants have also targeted the Red Cross in the past – its office in Jalalabad was attacked in 2013.

IS announced it was expanding into Afghanistan in January 2015 and has secured footholds in parts of eastern Nangarhar province, on the border with Pakistan.

But Afghan troops and the Taliban have prevented them from moving permanently beyond that, observers say.

Since mid-2016 the group appears to have switched tactics, launching a series of deadly attacks against Shia Muslims and others in Kabul and bombing a mosquein the northern province of Balkh, neighbouring Jowzjan, in October.

On Wednesday, IS said it had carried out an attack at the Supreme Court in Kabul a day earlier, killing at least 20 people.